There are 3 main ways to get USDtz
In most cases you'll get your USDtz from an exchange. Dexter is the main Tezos DeFi exchange, but more are coming. Early on this would be a great option for trading 'small amounts' and growing depth capacity over time..
If you want to buy USDtz for USDC 1-1 without slippage or exchange fees on, or if you want to buy enough USDtz in order to supply Dexter pools , and it would be prohibitively 'slipping' to buy such a large amount on the exchange itself, using a Mintery would be a better option.
If you don't want to go through a Mintery, and would rather mint on your own, then you may qualify to enroll as a minter or Mintery yourself. This is a particularly good choice if you have a Tezos baker in good standing.